linux-kernel - Re: [PATCH 11/20] blkio: Some CFQ debugging Aid

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Date:	Wed, 04 Nov 2009 13:52:51 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com,
	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	ryov@...inux.co.jp, fernando@....ntt.co.jp, s-uchida@...jp.nec.com,
	taka@...inux.co.jp, guijianfeng@...fujitsu.com,
	balbir@...ux.vnet.ibm.com, righi.andrea@...il.com,
	m-ikeda@...jp.nec.com, akpm@...ux-foundation.org, riel@...hat.com,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 11/20] blkio: Some CFQ debugging Aid

Vivek Goyal <vgoyal@...hat.com> writes:

> o Some CFQ debugging Aid.

Some CFQ debugging aids.  Sorry, I couldn't help myself.

> +config DEBUG_BLK_CGROUP
> +	bool
> +	depends on BLK_CGROUP
> +	default n
> +	---help---
> +	Enable some debugging help. Currently it stores the cgroup path
> +	in the blk group which can be used by cfq for tracing various
> +	group related activity.
> +
>  endif # BLOCK
>  

> +config DEBUG_CFQ_IOSCHED
> +	bool "Debug CFQ Scheduling"
> +	depends on CFQ_GROUP_IOSCHED
> +	select DEBUG_BLK_CGROUP

This seems wrong.  DEBUG_CFQ_IOSCHED sounds like it enables debugging of
CFQ.  In your implementation, though, it only enables this in tandem
with the blkio cgroup infrastructure.  Please decouple these things.

> +#ifdef CONFIG_DEBUG_BLK_CGROUP
> +	/* Store cgroup path */
> +	char path[128];
> +#endif

Where does 128 come from?  What's wrong with PATH_MAX?

Cheers,
Jeff
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